Fast Road Use - What Improvements can I make?

[carrierdave]

Good morning gentleman,
I am currently rebuilding my Twink and would like some advise on mild tuning for road us.
I have a standard +2 engine, pre S130, and have so far hand the flywheel lightened and the complete bottom end balanced.

My next thought was to expand the inlet valves out to the big valve size and then have the exhaust ports taken out to match the manifold. Also I was thinking of taking 30 thou off of the head to increase the compression ratio?

What other small changes could I make to improve the general acceleration and bottom end punch of this engine.

Thanks

Dave

[Dag-Henning]

Dave, - a cam-change would be the natural thing following yr bigger valves etc. Don't go for something "race-like", but for inst. "Sprint"-cams would make a noticable difference ! Then a rolling-road treatment in the end.(!!)
DH

[rgh0]

Dave

Sprint cams and valves and a clean up of the ports combined with sprint carb specs ( eg 33 mm chokes) and tubular exhaust headers and around 10 to 10.5 comp ratio and sprint advance curve for the distributor should give you around 130 hp which is what a blue printed sprint engine produces.

Trying to get more than 130hp out of a head without proper porting is an exercise in diminishing returns as the head just does not flow enough and you will loose you bottom end torque a lot faster than you pick up top end hp.

The next meaningful spec step in my opinion is around 150 hp but requires high lift short duration cams and a high lift valve train setup combined with full porting of the head and limited bottom end work to get the standard components to around 7000 rpm safely. However this is starting to get into serious $.

If you dont have a copy of the Dave Bean catalogue get it as it describes the various stages of development and whats involved in more detail.

Rohan

[carrierdave]

Thank you both for your comments. The cams are something I had considered.

One thing I have just noticed is that the engine I have, although having a 6 bolt crank, has the rounded shouldered main bearing caps.!!

Now I have a set of square caps from a 711 block ? should I use them? Will they fit? will they foul the sump? Will I need to get it line bored?

I assume that I will need to go for the longer 711 bolts as a minimum.

Thanks

Dave

[rgh0]

Dave

The older style round caps are fine unless your trying to build a 8000 rpm plus engine. They were normal on all twin cams except perhaps the last few made in 73 /74. To install the square shoulder caps you would need to line bore the block and use suitable longer bolts, otherwsie no other issues fitting the square caps. However not worth the effort unless you are aiming to build a high rev engine and planning to spend a big chunk of cash on a steel crank, special rods and forged pistons.

Rohan

[Dag-Henning]

Dave, - yes, you would have to get the assembly line-bored. Don't bother unless you aim at 8000 rpm for the rest of the day.....
The "Cortina-block" for 1967, - the 2731M type had the 6-bolt/ round cap configuration, and would be strong enough for the road. (!)
DH

[carrierdave]

Thanks for the note Rohan ? Cash is certainly scarce at the moment so I will stick to the round caps.

Do you have any suggestions on aftermarket cams? I was thinking about sending mine off to get them re-profiled ? what do you think?

Thanks

Dave

[rgh0]

Dave

Dont know where you are located so hard to give a recommendation. Most of the reputable cam suppliers around the world can do a sprint style grind. The also have variations claimed to give more power on the standard or near standard valve lift, most will not give much more without doing signficant porting and most sacrifice big torque for a little more top end power.

Depending on the cams you have now you may or may not be able to get the sprint type profile out of them with just a slightly smaller base circle that you can compensate for with thicker shims. You would need to talk to the cam grinder you choose to find what they can do and figure out what this means for the shims you have to use. Possible to build up by spray welding and regrinding the cams to retain the standard base circle relatively cheaply but this introduces some other metalurgical problems that it is best not to have to face unless you really have to. Nothing impossible just tricky to get it all done right.

Rohan

[cliveyboy]

Go for uprated head bolts by ARP.
The company that rebuilt my twincam said they are a must have.

Other options to consider:- vernier timing pullies, water pump conversion,
head ported and flowed. Unleaded valve seats
Then when its all back together you can start thinking about rebuilding the carbs,sports air filters, new radiator, silicon hoses, electronic ignition, magnecor leads.

Clive

[bill308]

Dave,

The modifications described in this thread pretty mutch describe my S2 engine, with some exceptions.

The exceptions are that I currently have the early bottom end. Smaller con rod bolts on a 4-bolt crank and compression ratio somewhere between the stock and sprint specifications.

Modifications incorporated are large intake valves with a lot of attention to the seat area and the port throat was suitably opened up to accomodate the larger intake valves. The intake port was gently cleaned up and opened up to match the intake manifold. The exhaust ports were opened up to match the tubular headers. The combustion chamber was enlarged, where necessary, to equalize the volumes after a light skim cut to ensure flatness. The cams were properly degreed in after meticulouly determining TDC with a dial indicator. The crank, rods, and pistions were balanced to 0.1 grams. The crank was dynamically balanced and journel radii were ground to spec and shot peened. The crank mounted fan was removed and an electric blow thu fan was substituted. Stock SE carburation, 40DCOE-18 webers with 1.75 inch velocity stacks, are fitted. I'm unsure of Ignition timing at this time but remember advance came in early, but overall advance was limited per spec.

This combination works well. Low end torque is very good and the engine pulls well beyond 6800 rpm, although I seldom use it in this range.

I elected to go conservative in compression ratio, because I don't want to be a slave to high octane gas plus additives. Although I've never put it on a dynomometer, I can tell you the seat of the pants measurement is significant and the engine is noticibley stronger than the stock SE variant it started life as.

Future plans are to replace the Webers with Dellorto DHLA 40 E carbs with 33 mm chokes and possibly a higher lift cam with modest duration. I'm hoping the planed changes will lift me from the 130 hp range to the 140 hp range. All this on r+m/2, 93 otane pump gas. The car will push you back in the seat.

Bill

[forfenderjazz]

Reading this post brings back fond memories about the days when I was young and had lots of money to dump into my big valve twin cam. The money is staggering. Right now I have three kids and can't afford to build a twin cam, and there is a 28 thousand mile zetec two liter engine in the local paper for only 300 dollars! I'm going zetec with my +2. I can get lots of reliable power, cheap and it will burn regular grade gas! Good luck, though, Roy

[carrierdave]

Bill,
Thanks for the post. It was very interesting to hear what you have done and also that you gained something from it.
I have had a big concern over what can be gained from all of these modifications and the last thing I wanted to do is have all the worked carried out without any significant change.

When you read the Miles Wilkins book it leaves you wondering where the datum point is for the engine in terms of BHP. Was it 108 or 118bhp and what was the true increase in BHP when they introduced the S130?

Has anyone had a dyno test carried out on there engine and what sort of BHP did you get at the wheels?

Thanks

Dave

[bill308]

Dave,

One other mod I forgot to mention was I installed a low inertia, Tilton, aluminum flywheel. A machined cast iron or steel flywheel would likely achieve the same results. Just make shure the end product is crack checked. The normal place to remove material on this type of wheel, is a radial cut on the flange below the ring gear. It's the rotational inertia (reduces polar moment of inertia in techno speak) one seeks to reduce, not necessarily the overall weight. This can have a dramatic beneficial effect on the acceleration capability of the engine/car. The down side is that it puts a premium on low end torque for road use. The up side is that if you have the low end torque, clutch wear shouldn't be a problem. Increased wear incured from a normal standing start will be minimal, with sufficient torque, and normal gear changes shouldn't result in any additional wear. Down shifts should result in less wear.

Bill

[Dag-Henning]

Excuse me guys ; - but why would you lighten your flywheel for road use ?? I see nothing but disadvantages from that on a road car, but will do my best to be open-minded....
I have a super light one on my racing car, but for my roadcar ; no way.
Dag

[carrierdave]

What I am trying to achieve is an engine that gives me quick acceleration/deceleration and is fast between corners/roundabouts.
It was suggested to me that lightening the flywheel would give me an engine that would do this; Rev freely and quicker as well as an engine that would decelerate quicker.

With the reduction in power require to turn the flywheel and the reduction in inertia when slowing down his suggestion seemed logical.

Dave